The present invention relates to a buoyancy unit with controlled heave, and more particularly to a unit of this kind intended to hold the deck of a floating oil rig up out of the water.
Floating oil rigs are subjected to wave motion which, during the passage of a wave, alters the draught of the rig. This variation causes the rig to move along the vertical axis, as the rig attempts to maintain constant draught.
Each sea has its own geographical conditions which give the wave motion associated characteristics: mean height of the waves and frequency of the wave motion. The shape and dimensions of a rig give a specific response time during the passage of a wave. In order to avoid problems of resonance it is necessary for the natural periods of the wave motion and of the rig to be sufficiently different.